Thermoelastic Behaviour and Higher‐Order Elastic Constants of Ionic Crystals

The relationships are given between thermoelastic properties and higher‐order (third and fourth order) elastic constants for twenty alkali halides with NaCl and CsCl structures, and for four alkaline earth oxides viz. MgO, CaO, SrO, and BaO crystals. Expressions for thermoelastic quantities such as the Grüneisen parameter and its volume derivative, Anderson parameters, and thermal expansion coefficient, are obtained in terms of higher‐order elastic constants. These expressions provide a new method for estimating thermoelastic quantities from higher‐order elastic constants. Calculations are performed using an interionic potential model which takes account of three body interactions, van der Waals interactions, and overlap repulsive interactions upto second neighbours. The results are discussed and compared with experimental data.